1. Field of the Invention
The present invention relates to a method for processing image data and an apparatus therefor, and more particularly to such method and apparatus for synthesizing at least two image signals.
2. Description of the Prior Art
As an example of high-speed image synthesis there is already known that employed in the field of television in which a synthesized image can be obtained by receiving and storing the image signal of a program in a random-access frame memory while receiving and reproducing another program, reading the thus stored signal at a determined position in said other reproduced program, and switching two signals by a switching circuit. In such case said switching circuit can be composed of an analog switch since the image synthesis is basically effected between analog signals. Such conventional method is however not applicable to the run-length encoded signals obtained for example in facsimile devices.
As already known, the run-length encoding is employed for compressing the amount of continuous signals such as image signals. For example 320 consecutive white pixels, conventionally requiring a memory capacity of 320 bits, can be compressed in said encoding to less than 20 bits, i.e. several bits indicating white pixels and also several bits representing "320". The rate of compression can be further increased by so-called modified Huffman code with variable length. It has been difficult in the known art to synthesize such encoded and compressed signals.
Also computer processing, such as synthesis, of such encoded image signals has been quite slow.